Specialty gases are often used in numerous process steps during the fabrication of advanced semiconductor devices. Gases with low vapor pressures at room temperature, are typically stored as liquids in a container, under their own vapor pressure, and many of them are very hazardous. In many instances, the process gases may have to be transported along a gas distribution or piping system to a reactor across a manufacturing facility. Changes in the ambient air around the piping system may affect the physical state of the gas inside the piping system. For example, a temperature decrease or a pressure increase may cause the gas to liquefy and result in adverse effects on the performance of the gas distribution system, including pressure fluctuations, reduced component life and in some cases, dangerous chemical reactions.
Efforts to monitor liquefaction—i.e., a change from a gaseous to a liquid state, of such gaseous materials include the use of optical devices that detect liquefaction by light scattering. However, such devices tend to be expensive and only detect liquid formation after liquefaction has occurred. Thus, the need exists for a more cost-effective method of monitoring liquefaction before it occurs.